In the past, there has been known a projector, which modulates a light beam emitted from a light source to thereby form an image corresponding to image information, and project the image on a projection target surface such as a screen in an enlarged manner. As such a light source, there is often used a light source lamp (a light emitting tube) such as a super-high pressure mercury lamp provided with a light emitting tube having a discharge space inside with a pair of electrodes and a light emitting substance encapsulated.
Here, in the rated lighting state in which the light source lamp is lighted at the rated power, the mercury in the discharge space exists in the form of vapor. It can be said that this state is a state exceeding a saturation threshold level. In contrast, in the case of, for example, displaying a dark image, if the lamp electric power is reduced to thereby decrease the luminance of the light source lamp, the temperature in the discharge space drops to be lower than in the rated lighting state and becomes lower than the saturation threshold level, and thus the mercury vapor is compressed to thereby cause the state in which the pressure in the discharge space is lowered. In such a state, it becomes difficult for the halogen cycle, in which the tungsten evaporated from the electrode returns to the electrode, to appropriately function, and thus it becomes easy for the blackening, in which the tungsten is attached to the inner wall of the light emitting tube, to occur. Such blackening lowers the luminance of the light source lamp to thereby shorten the product life of the light source lamp.
Therefore, there has been known a projector (a projector system) capable of preventing the blackening from occurring (see, e.g., PTL 1).
In the projector described in PTL 1, when the period of a dimming operation mode for lighting the light source lamp with low lamp electric power exceeds a predetermined time, there occurs transition to a restoring period in which the lamp electric power is increased to be higher than the saturation threshold level. Thus, the temperature in the discharge space rises to thereby eliminate the blackening accumulated, and therefore, a further operation of the light source lamp in the dimming operation mode becomes possible.